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cmorris975
02-12-2008, 09:43 AM
I'm just wondering what you all think about Bernoulli's principle being credited as the main way a wing creates lift on aircraft. Is it passe? I read somewhere that under Bernoulli's principle alone it would require a Cessna 172 to reach 400 mph before it could get off the ground. The reason I ask is that I just bought an aerodynamics textbook and it is decribing Bernoulli's principle as the main force that generates lift; I thought that was out-dated?

Chris

PhantomKira
02-12-2008, 11:00 AM
Not that I'm aware of. I've a Bachelors Degree in aviation, and private pilot license, and Bernoulli's Principle was what they were teaching us. This was less than five years ago.

The biggest problem with using BP as the only way of describing the production of lift on wings is explaining how it is that balsa wood aircraft fly. They certainly don't seem to have much camber in the wing, so it might just be angle of attack alone that gets them airborne. We had long arguments in school about which principle was the correct one. I suspect it might be a bit of both.

For example, if you look at the mounting of the wing of a Cessna 172, it isn't zero degrees to the thrust line. It's actually canted up a few degrees, so that airflow hits the bottom of the wing first.

buzzsaw1939
02-12-2008, 11:05 AM
Never heard that one Morris!... I would be suspect of where you read that. http://forums.ubi.com/images/smilies/blink.gif

Korolov1986
02-12-2008, 11:08 AM
With enough force and energy, you can make anything fly.

cmorris975
02-12-2008, 11:27 AM
I read it (among other places) in a book by Ira Flatow, the science correspondent on NPR. Supposedly the popularity of the Bernoulli Principle comes from a World War II wartime push to explain flight to the masses in a simple way. There are those, especially in recent years, that say this is incorrect; that the majority of the lift from a wing is generated from its angle of attack and the downstream coming off the tail end of the camber.

*shrug* I am just starting to learn about this stuff.

Patriot_Act
02-12-2008, 11:35 AM
PhantomKira, if you do have a degree and they were teaching you Bernoulli's principle alone then you were in need of a new school.
Bernoulli's principle is the by product of the Coanda effect.
It is the coanda effect that diverts the airflow down to create the equal and opposite effect, lift.
If Bernoulli's principle was the reason wings work, then supercritical airfoils could not work.

Bernoulli should not be dissed. He was a brilliant man that worked in the 1700s
many years before flight was more than a dream.

Henri Coanda was the guy who first described how fluids will follow the surface
of objects and as a result, flow over the top and bottom of a wing

If you are a fanatical believer in Bernoulli's principle simply stand under a helicopter
or behind a propeller. They are rotary wings. You will then be shown clearly that
wings are air pumps and Bernoulli was a nice old Italian fellow that showed us how to make
better atomising perfume sprayers.

So, the above post is correct. It is the effect of AOA weather you have a symetrical or asymetrical airfoil.
The Bernoulli's principle myth is kind of like the myth about P-39s lacking a supercharger.
The old bad myths never let go. (Yes folks, all P-39s had a supercharger).

P.A.

PhantomKira
02-12-2008, 12:01 PM
Ah, no, not hardly, just part of it! I've gotten into other things, and it's kinda fuzzy now, so perhaps I'm remembering it from how the engine works (float carburetor type).

As the saying goes, if you don't use it, you loose it. It's a bit fuzzy what's where anymore as I haven't been in a plane in quite a while... (Time and money, and lack thereof, you know how it goes...) Ah well. Point taken! http://forums.ubi.com/images/smilies/25.gif

buzzsaw1939
02-12-2008, 02:04 PM
Wow!... I had no idea that all those years I was flying on a myth, I guess I better go out and take my wings off, and put flat boards at a high angle of attack!

of coarse theres more to lift than Bernoulli's princible, thats a given!

To say that every pilot who learned to fly and studied the basic principle of lift was lied too, is the most ridiculus thing I've heard in years!

If you need recognition for studying air areodynamics, you got it!

But just remember, while guys like you were designing those wings, there was guys like me out risking our lives in those "myths"

Sorry guys, but that really ruffled my feathers! http://forums.ubi.com/images/smilies/16x16_smiley-mad.gif

Btw Morris.. what you read is correct about the majority of lift, and the air comeing off the tail camber, but most pilots don't worry about that stuff in every day flight, they have too many other things to worry about. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

Patriot_Act
02-13-2008, 02:23 AM
Originally posted by buzzsaw1939:
Wow!... I had no idea that all those years I was flying on a myth, I guess I better go out and take my wings off, and put flat boards at a high angle of attack!

of coarse theres more to lift than Bernoulli's princible, thats a given!

To say that every pilot who learned to fly and studied the basic principle of lift was lied too, is the most ridiculus thing I've heard in years!

If you need recognition for studying air areodynamics, you got it!

But just remember, while guys like you were designing those wings, there was guys like me out risking our lives in those "myths"

Sorry guys, but that really ruffled my feathers! http://forums.ubi.com/images/smilies/16x16_smiley-mad.gif

Btw Morris.. what you read is correct about the majority of lift, and the air comeing off the tail camber, but most pilots don't worry about that stuff in every day flight, they have too many other things to worry about. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

Hate to pop your bubble Buzz, but no one has credited the Bernoulli's princible for the operation
of an airplane's wings since Henri Coanda described the math of the effect beraing his name in 1910.
No one except for high school science books and sadly the USAF museum site!
Yes, flat plywood can provide lift but lacks the required structure to provide a safe wing.
The airfoil shape is very important as a means to create
a path for the fluid (air) to flow over a wing's surfaces without seperation aka turbulence.

Note that a supercritical airfoil has a longer path for the flow on the lower surface.
Supercritical airflows give a better lift to drag than the best conventional airfoils
especially near the trans sonic flight regime. If Bernoulli's princible were the source of lift
then a supercritical airfoil would never get off the ground.
Many aircraft designed since the early 1980s have supercritical airfoil wings.

Bernoulli's principle is quite accurate in describing the effects on air passing over a surface
having a drop in pressure as velocity increaces. What Bernoulli did not understand is that the drop in air pressure
is the result of the fluid (air is a fluid) adhearing to the surface of the curved surface (venturi).

"Wow!... I had no idea that all those years I was flying on a myth" You are absolutely correct on this point.
You had no clue as to what was really providing the lift.

Newtons third law can not be bypassed.
Third Law
Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This law is often simplified into the sentence ---"Every action has an equal and opposite reaction".----

Wings are little more than air pumps providing downward thrust.

P.A.

buzzsaw1939
02-13-2008, 04:55 AM
I knew it! http://forums.ubi.com/images/smilies/88.gif A young chart monkey with no world experience, who has all the answers, and is willing to take on millions of experienced airman and tell them they have been wrong, you haven't said anything that we don't already know.

Where do you think we got our certificates? out of a crackerjacks box?

"I had no clue as to what was providing the lift" http://forums.ubi.com/images/smilies/88.gif

Nice catch kid! you caught a big one!

NAFP_supah
02-13-2008, 05:14 AM
Originally posted by buzzsaw1939:
I knew it! http://forums.ubi.com/images/smilies/88.gif A young chart monkey with no world experience, who has all the answers, and is willing to take on millions of experienced airman and tell them they have been wrong, you haven't said anything that we don't already know.

Where do you think we got our certificates? out of a crackerjacks box?

"I had no clue as to what was providing the lift" http://forums.ubi.com/images/smilies/88.gif

Nice catch kid! you caught a big one!

In ground school I was told exactly the same as Patriot_Act explained. What he said is right, the bernoulli effect isnt the sole source of lift. Sad to see that your world experience left you with such a deffective attitude. Perhaps you need some attitudal recurrency training.

Skoshi Tiger
02-13-2008, 05:52 AM
RAAAID where are you when we need you????????


"the lift generated by the impact of air on the bottom surface of the wing amounts to only a fraction of the lifting force needed to sustain the aircraft in flight. More than 75% of the lift is caused by the lower pressure above the airfoil. the wing is not so much pushed up from below by excess air pressure as pulled up from above by low air pressure" (Aviation/Aerospace fundamentals, Jepson Sanderson)

Increasing the angle of attack increases lift by causing the molecules of air to travel further over the top of the wing than the bottom, thus increasing the lift caused by the Bernoulli effect.

Super critical wings, flat plates and the flat wings of balsa aircraft still generate lift using the Bernoulli effect. Helecopter rotors and propellors generate lift (up and forward respectively) using the Bernoulli effect.

Any lift that is created by the striking of air molecules that strike the bottom of the wing has the downside of producing drag on the aircraft. (thats why jet fighters need whopping great jet engines to fly - they need them to overcome the drag induced by their flat wings and the high angles of attack needed to produce lift - have you ever seen a video of a F104 starfighter taking off)

buzzsaw1939
02-13-2008, 06:18 AM
Originally posted by NAFP_supah:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by buzzsaw1939:
I knew it! http://forums.ubi.com/images/smilies/88.gif A young chart monkey with no world experience, who has all the answers, and is willing to take on millions of experienced airman and tell them they have been wrong, you haven't said anything that we don't already know.

Where do you think we got our certificates? out of a crackerjacks box?

"I had no clue as to what was providing the lift" http://forums.ubi.com/images/smilies/88.gif

Nice catch kid! you caught a big one!

In ground school I was told exactly the same as Patriot_Act explained. What he said is right, the bernoulli effect isnt the sole source of lift. Sad to see that your world experience left you with such a deffective attitude. Perhaps you need some attitudal recurrency training. </div></BLOCKQUOTE>

Why don't you read my post a little more carefully, "all pilots" I repeat "all pilots" know what he is saying, it's part of our training, he didn't say it's not the sole source of lift, he said it's a myth, and that I have no idea what kept me in the air! http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

attitudal recurrency training?..more bait? http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

Perhaps you guys need some retraining on respect, or do they not teach that anymore?

Viper2005_
02-13-2008, 12:15 PM
Bernoulli may be paraphrased thusly:

Ptotal = Pstatic + Pdynamic (+ potential energy which we normally forget in aerodynamics)

Pdynamic = 0.5*roh*v^2

This is true provided that the flow is incompressible, which is a reasonable simplification (error ~1% or less) for air at Mach numbers less than 0.2 or so.

If one then assumes that the total energy of the flow is unaffected by the wing (i.e. friction is insignificant, or if you prefer, the Reynolds number is large) then it follows that the total pressure is constant.

Therefore it is possible to mathematically transform a velocity distribution into a pressure distribution, and therefore by integrating the pressure distribution over the aerofoil it is possible to calculate the resultant force, which if you're in the business of designing or flying aeroplanes will hopefully be pointing in a generally upwards direction.

Bernoulli doesn't directly say anything about the velocity or pressure distribution over the an aerofoil. He just says that the two are mathematically interchangeable if the flow is incompressible.

Unfortunately, the kind of sloppy text books which say things like:


The air passing over the top of the wing has further to go than the air passing underneath and must therefore move faster...

have a nasty habit of attributing this rubbish to Bernoulli, who as far as I know never said anything of the sort.

See also:

http://en.wikipedia.org/wiki/Bernoulli%27s_principle

M_Gunz
02-13-2008, 01:33 PM
Buzzsaw, you know how long downwash from a big jet landing can ruin a small plane's approach?
That's because wings do set air in motion opposite the lift, however they do it.

I never knew that explanations given to pilots actually made the plane fly.
The explanations are good and complete enough to use when flying.
I've seen the same with shooting, it didn't make the marksman any less accurate.
He just wouldn't make a really good gunsmith.
When's the last time you had to *calculate* where your lift was coming from?

I've made gliders that flew fine, different sizes and shapes, the book that got me started
gave the Bernoulli Effect explanation and even ways to prove it works but no calculations
used it. You build and test and see what you can get, if it flies then it must work how the
book says, right?

Something I am sure of is that if by Bernoulli it would take 400mph to get a 172 in the air
then that explanation would have been dropped long ago! Airspeed over and under wings has
been checked and tested since, I would guess the Wrights if not long before.

Bernoulli effect alone does not tell me that the wing throws air downward enough to push up.
Without that I cannot fly, it would violate physics.

Gibbage1
02-13-2008, 02:32 PM
Bernoulli works well for basic flight and basic wing aerofoils, yes, but there is a lot more at work then just the Bernoulli effect. Once you get faster, and go outside beyond standard wings and aerofoils, there are a lot more things that need to be considered.

There is boundry layers, ground effect, and wing profile changes for landing and takeoff that effect the wing.

There are also vorticies generated off of the wing tips that will crash small aircraft fallowing a large aircraft, now downward draft's. Wing tip fins like those found on large passenger jets can harnis these vorticies.

At high speed, you also have the area rule to consider, along with many other aspects of the sonic shock wave.

The point is, Bernoulli is a basic principal, and its the biggest governing factor on most basic aircraft. Yes, there are other factors at play, but none bigger then the Bernoulli effect on almost all aircraft. Im sure there are exceptions to the rule.

buzzsaw1939
02-13-2008, 02:58 PM
Gunz.. If I understand you correctly, you are right!

I can't do the numbers any more like you young guys, I won't even try. if I wanted too, I could draw you diagrams to explain it all, you would see it all very clearly.

Wing tip vortice is what dumps a plane on landing behind another, low pressure on top, and high pressure on the bottom with high angle of attack, when it leaves the tip, it mixes into a vortice.

Actually, I would go so far as to say Bernoulli's principle has nothing to do with flight, it is simply air moveing over any flat surface creates a low pressure! hince the distance of the top surface vs the distance on the bottom, air moves faster on top to equalize it self when it rejoins at the trailing edge, AOA adds to the lift with positive pressure on the bottom, (untill it stalls with to much drag), very basic to help student pilots get a start on understanding why a wing lifts, thats the way I tought it, and demonstrated it, and I'm sure they still are!

I thought I made it clear above, that theres many factors at work!

As for the downward pressure, let me tell you this, many pilots who were shot up, looseing fuel, trying to get back over water, would fly in ground effect so they could throttle back and conserve fuel, it does work, I've done it!

I'm just a little confussed as to why guys who read books on areonotics, seem to think that pilots don't know anthing about it, to the point of insults! what hubris! It doesn't impress me at all.

When some snot nosed kid, with quotes from a book and a calculator, tells me I don't know what makes a wing fly, he's going to get a laugh from me, and a few words to boot.

I'm not in this forum to prove anthing to any body, if I can help, I'll do it, nothing more, nothing less.

I'm not an areonatical engineer, I'm damn good pilot with a perfect record, and I've never lost a student for lack of nowledge.

Korolov1986
02-13-2008, 03:17 PM
Proof that fluid dynamics are a bunch of hogwash:

Helicopters fly.

buzzsaw1939
02-13-2008, 03:24 PM
I'll drink to that!.. http://forums.ubi.com/images/smilies/winky.gif

Gibbage.. I just saw your post, well said!

DuxCorvan
02-13-2008, 03:30 PM
Everybody knows the planes fly because the moon is magnetic. http://forums.ubi.com/images/smilies/16x16_smiley-indifferent.gif

M_Gunz
02-13-2008, 04:00 PM
Show me AOA in any of Bernoulli's work.
Then look over the basic Lift Equation.

For sure the relative pressure of air below and above the wing does make lift but how you
aim the wing makes a huge difference in lift.

There's an old picture of a Gulfstream flying just over cloud and this huge trench in the
cloud behind it, not two ruts but one flat trench. Should I also believe that props only
push air behind at the tips?

If I go by Coanda then I can see that the wing causes air mass that is going up to go down,
a shift in momentum that is also lift. He made that work for a short time about 100 years
ago, before the plane caught fire. Bernoulli's work also played in that.

Personally I think that you have many factors that interplay totally, not one without the
other. At any AOA that differentiates airflow between top and bottom to make Bernoulli
effect you will also get air pushed down. If you work it out from an energy POV I bet that
Bernoulli effect MUST BE equal to 3rd Law of Motion effect since they are part of the same
system.

Skoshi Tiger
02-13-2008, 04:41 PM
Originally posted by M_Gunz:
If you work it out from an energy POV I bet that
Bernoulli effect MUST BE equal to 3rd Law of Motion effect since they are part of the same
system.
+1000

buzzsaw1939
02-13-2008, 04:47 PM
Gunz... I'm not sure who your addressing.

If it's me, we're saying the same thing, mines just simplefied. read it again please. http://forums.ubi.com/images/smilies/blink.gif

Besides Dux is right, it's the moon!

BSS_Sniper
02-13-2008, 05:13 PM
I think that all of you should stop working at your reg jobs and start designing and flying aircraft. lol

Sergio_101
02-13-2008, 06:50 PM
Gibbage, incorrect. Bernoulli' observations
are a by product of the Coanda effect.
Bernoulli did a nice job laying the foundation
for carbs and air conditioning.

This horse got whipped dead a few years back.
Bernoulli' principles do not apply in flight mechanics
except where there are interruptions in the boundry layers, like spaces at the interface
of the wing and flight controls, and/or bullet holes http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Patroit act is fight on the money. Except he gives
the Bernoulli principle more credit than it deserves.

Henri Coanda got it right. Yes you need carefully\countoured surfaces to prevent turbulence and loss of the surface flow.

And there are many airfoils that would drive you right
into the dirt if wings worked by Bernoulli alone.
As Patriot Act pointed out, a supercritical airfoil
could not work under Bernoulli's laws.

Supercritical airfoils have better drag to lift ratios
at all airspeeds than conventional airfoils.
Not just high speeds.

Yup children, wake up. Bernoulli is just an old myth.
No educated areospace engineer would make the mistake to credit Bernoulli for a wing's lift.

Yes folks, we may have a few fakers posting here, suprised?

Oh yes, I am NOT Patroit_Act.
Any Mod can verify that by my IP number, thank you.

Got to say that Patroit Act did a GREAT job spanking
the Luft Cryers in the various Me-262 threads.
I was away.....

Threads are locked now, bummer.

Sergio

buzzsaw1939
02-13-2008, 07:09 PM
Fakers and children... mmmm, I guess thats my que to put my tail between my legs and slink away, I've been found out by an authority who reads books.

Oh the shame! http://forums.ubi.com/groupee_common/emoticons/icon_rolleyes.gif

M_Gunz
02-13-2008, 07:22 PM
Originally posted by buzzsaw1939:
Gunz... I'm not sure who your addressing.

If it's me, we're saying the same thing, mines just simplefied. read it again please. http://forums.ubi.com/images/smilies/blink.gif

That's twice you've said that. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif
I was just doing a little more reasoning and trying to clear up my picture.
I know the Bernoulli Principle works cause I've used it in and out of labs as well as gliders.
It's demonstrable on models, clearly. Blow air only over the wing top and she rises.

It's just that the principle alone does not explain flight though I *strongly* disagree with
anyone who doesn't think it has anything to do or it has little to do with lift!
For sure, You are NOT one of those people! http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif For certain we both believe it applies!


Besides Dux is right, it's the moon!

Now that's silly and you know it. I have yet to see an FAA phases of the moon effects on
flight chart!

M_Gunz
02-13-2008, 08:07 PM
Originally posted by Sergio_101:
Gibbage, incorrect. Bernoulli' observations
are a by product of the Coanda effect.
Bernoulli did a nice job laying the foundation
for carbs and air conditioning.

Daniel Bernoulli born in 1700 and amongst other things determined a lot about fluids and energy,
you call his 'observations' a byproduct of the Coanda Effect circa 1910?

Pressure of water run through a pipe varying with speed as a byproduct of fluids following
surfaces by a man who had to have studied Bernoulli's work?

In physics, hydraulics and fluid dynamics, Bernoulli's Principle states that for an incompressible fluid (e.g. most liquids), with no work being performed on the fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's gravitational potential energy.[1] Bernoulli's Principle is named in honor of Daniel Bernoulli.

You can't go by impressions gained from any book you happen to pick up. (http://en.wikipedia.org/wiki/Bernoulli%27s_principle)


A common misconception about wings

There is a misconception about the applicability of Bernoulli's Principle to the generation of lift on the wings of aircraft. Some people believe that Bernoulli's Principle cannot be used to explain the lift generated by the wing of an aircraft in flight. It appears to have arisen inadvertently from introductory books about aviation and flying.

Stick and Rudder

For example, in 1944 Wolfgang Langewiesche [9] wrote Stick and Rudder, an introductory text for aviation enthusiasts and student pilots. Langewiesche aimed to explain the operation of aircraft in simple terms that would be factual but easily understood by newcomers to aviation. He particularly strove to avoid concepts that were outside most people's day-to-day experiences. "Forget Bernoulli's Theorem" he wrote. [10]
Langewiesche was a skilled aircraft pilot and instructor. He did not doubt the validity of Bernoulli's Theorem (Principle), nor its applicability to aircraft, but he did recognise that any aspiring pilot need not struggle to grasp the Theorem in order to understand the basics of operation of an aircraft. Langewiesche wrote [11] "Bernoulli's Theorem doesn't help you the least bit in flying. While it is no doubt true, it usually merely serves to obscure to the pilot certain simpler, much more important, much more helpful facts."


Understanding Flight

As a second example, in 2001 David F. Anderson and Scott Eberhardt wrote Understanding Flight, [13] another introductory book about aviation and flying. In their Introduction, Anderson and Eberhardt acknowledge Langewiesche's injunction "Forget Bernoulli's Theorem". They also say "The object of this book is to provide a clear, physical description of lift and basic aeronautical principles." Anderson and Eberhardt provide readers with an understanding of Newton's Laws of Motion, and avoid other more complex principles. In particular, they avoid any emphasis on mathematics. In their Introduction they say "It is our belief that all fundamental concepts in aeronautics can be presented in simple, physical terms, without the use of complicated mathematics. In fact, we believe that if something can only be described in complex mathematics it is not really understood. To be able to calculate something is not the same as understanding it."

That last sentence tells it all, those guys are dweebs when it comes to math and science.
I say so because the 'complex mathematics' explains more clearly what is going on than 100x
as many words will only less precisely. They don't know how to read the language (like a
LOT of members here) so they discount it (a subset of those members, the mouthy ones) and
write anyway.


Like Langewiesche, Anderson and Eberhardt do not dispute the validity of Bernoulli's Principle. They say "This reduced pressure causes the acceleration of the air via the Bernoulli effect". [14]


The acceleration of air around a wing, the lowering of air pressure, and the production of downwash all occur simultaneously. One does not cause the other. They are caused by the shape of the airfoil, its speed relative to the air, its orientation to the passing air, and even the viscosity of air. At this point, Anderson and Eberhardt may have added unnecessary complexity by implying that aviation enthusiasts and aspiring pilots need to understand which comes first, acceleration of the air, lowering of its pressure, or the production of downwash. Bernoulli's Principle says only that a change in pressure, a change in speed and a change in elevation all occur simultaneously. Bernoulli correctly avoided saying one was the cause and the others were the effect.

That's the difference between dweebs and scientists. The dweebs see only one bit at a time.
But they will tell us to blow off those who they can't follow the work of much less criticize.
Did they even look at the Kutta-Joukowski theorem? Probably for about 5 seconds! OH NO! It's
got MATH in it! Can't beeeee trooooo!

Patriot_Act
02-14-2008, 04:34 AM
Truth be known coanda and Bernoulli are linked.
Bernoulli described effects caused by the Coanda
effect, though Henri coanda was 200 years later.
Yes Gunzz, even a fluid blown through a tube.
Want to see Bernoulli in action?
Use a Jai alai style ball thrower and watch the ball curv
upwards in dramatic form.
Airflow over both surfaces is equal. Coanda can not be at work?
Not quite.
What is happening is the ball is rapidly spinning with it's axis of rotation
90 degrees to it's flight path.
Air is effectifly pumped over the top of the ball as a result of the leading
rotating in the up direction creating increased airflow over the top
and a low pressure area on the top. But that air is deflected down
after passing over the top. Coanda again.

My point, wings work because of the Coanda principle.
But Bernoulli and his improved perfume sprayers can never be ignored.
Just think, he did all this in the early 1700s!

Dead thread time, no more point in posting.

P.A.

Vanderstok
02-14-2008, 05:35 AM
Funny, I have an MSc in aeronautics and have never heard of this Coanda! Surprised?

I just looked up Coanda on Wikipedia. It appears he descirebed the Coanda "effect" ,which I think is an OBSERVATION and doens't really explain anything by itself. In my studies these observations were covered with theories for viscous flows and the Boundary layer effect, which explains why I never even heard about Coanda (my loss though,I think he deserves his place in aeronautical history).

Bernoulli developed a mathematical THEORY for incompressible fluids which still holds today. The reality is that we are not dealing with an incompressible fluid, so his theory alone will not explain everything about lift, but it still is a good starting point when you study aerodynamics.

buzzsaw1939
02-14-2008, 07:07 AM
Gunz... Don't you know, old people repeat themselves a lot!.. http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif thanks for trying to clear this mess up, you too Vanderstok! and all the others that contributed to my not thinking I'm totally senile,.. yet!

I guess I better learn to keep my mouth shut and remember that I don't have the communcation skills I used to, all I wanted to say to Morris, was that I questioned where he got that info, (it's all your fault Morris! http://forums.ubi.com/images/smilies/16x16_smiley-mad.gif) .. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

Morris..?......Mooorris,....anybody seen Morris?

M_Gunz
02-14-2008, 09:53 AM
Originally posted by Vanderstok:
Funny, I have an MSc in aeronautics and have never heard of this Coanda! Surprised?

I just looked up Coanda on Wikipedia. It appears he descirebed the Coanda "effect" ,which I think is an OBSERVATION and doens't really explain anything by itself. In my studies these observations were covered with theories for viscous flows and the Boundary layer effect, which explains why I never even heard about Coanda (my loss though,I think he deserves his place in aeronautical history).

Bernoulli developed a mathematical THEORY for incompressible fluids which still holds today. The reality is that we are not dealing with an incompressible fluid, so his theory alone will not explain everything about lift, but it still is a good starting point when you study aerodynamics.

Stanley Schmidt had apparently met Coanda at some time on a professional level (he's an
engineer that also edited Analog IIRC) as he had very good things to say about Coanda's
contributions to fluidics for machine control including designs for fluidics switches.

Coanda might have made a bigger impact on flight if he had backers but he did not. Instead
he'd get set back trying to do everything on his own money, the word some used was ruined.
It's a shame as I've seen well backed men produce and sell junk.

You never heard or read about the guy that made the plane that blew air over the wings for
both thrust and lift? Great idea except when he did it the exhaust was too hot for wood
and canvas. There have been designs promoted since, fixed wing and rotary to pump high
pressure bleed air from turbines in such a manner but I know of none past drawings stage.

M_Gunz
02-14-2008, 10:50 AM
Originally posted by Patriot_Act:
Truth be known coanda and Bernoulli are linked.
Bernoulli described effects caused by the Coanda
effect, though Henri coanda was 200 years later.
Yes Gunzz, even a fluid blown through a tube.

Fluid flow through a tube describes the Coanda Effect just HOW?


Want to see Bernoulli in action?
Use a Jai alai style ball thrower and watch the ball curv
upwards in dramatic form.
Airflow over both surfaces is equal. [QUOTE]

No it's not. I can do the same with baseball or tennis or ping pong.
Airflow differs between one side of the spin and the other and can be greater than the speed
of the ball, esp in ping pong.

Here, NASA has a demo for you. (http://www.grc.nasa.gov/WWW/K-12/airplane/bball.html)

[QUOTE]Coanda can not be at work?

You think for one moment that Bernoulli Principle and Coanda Effect are exclusive, can only
have one and not the other? Interesting.


Not quite.
What is happening is the ball is rapidly spinning with it's axis of rotation
90 degrees to it's flight path.
Air is effectifly pumped over the top of the ball as a result of the leading
rotating in the up direction creating increased airflow over the top
and a low pressure area on the top. But that air is deflected down
after passing over the top. Coanda again.

You describe Bernoulli Principle at work as well. But since he didn't define boundary layer
effects that means his work is not applicable?


My point, wings work because of the Coanda principle.

You have part of the picture and you want to call it the whole thing.
When did Coanda take credit for pressure differences due to flow speeds?
He described an Effect, not a Principle, about fluids following surfaces and then made many
applications of it.


But Bernoulli and his improved perfume sprayers can never be ignored.
Just think, he did all this in the early 1700s!

Dead thread time, no more point in posting.

P.A.

Bernoulli advanced understanding of conservation of energy greatly which if you want to
characterize his work by limiting it to perfume sprayers is your loss, not mine.

Lay a piece of paper on a table, hold the front edge down and blow over it.
The airflow follows the paper as Coanda Effect will tell.
The paper also rises, and I don't see where in the Coanda Effect that that is explained.

If the Bernoulli Principle was not at work then wing surfaces would not have to be fastened
down so well as they do, it would only be drag trying to remove them.

More to the point, pressure above and below the wing are measurable and the results have not
yet caused the aero-schools to throw the Bernoulli Principle out. They have included air
being diverted downwards which if you get lift, MASS HAS TO MOVE.

Sorry you feel so bad at school science being taught in simplified manner and want to change
how credit is given. So much used in practice today will just have to be thrown out.

OTOH you can get more upset at Kutta and Joukowski with their Circulation Theory taking credit
away from Coanda since that's getting more credit beyond the High School level.

You'd better go straighten Wikipedia out too, Coanda Effect is listed under Common Misconceptions about Lift. (http://en.wikipedia.org/wiki/Lift_%28force%29)

Patriot_Act
02-14-2008, 11:35 AM
Dead thread time, no more point in posting.

P.A.

M_Gunz
02-14-2008, 11:54 AM
Originally posted by Patriot_Act:
Dead thread time, no more point in posting.

P.A.

For you.

Holtzauge
02-14-2008, 12:25 PM
I think the Kutta condition (see link) and the circulation concept is useful. The circulation concept explains the vortice shedding along the wing and the massive lift induced vortices at each wing tip. Also: a wing in inviscous flow would not provide lift because the air would sneak back up the trailing edge and no lift would be produced. So don't curse viscosity (i.e drag) but be thankful every time you take off! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Kutta condition: http://en.wikipedia.org/wiki/Kutta_condition

M_Gunz
02-14-2008, 09:03 PM
Wingtip vortexes are a result of wing dihedral, air flowing up along the wing underneath
instead of straight back.

I've made exactly two gliders that had slight anhedral wings and could when thrown carefully
indoors (no wind) fly straight. The glide path was extremely shallow compared to others,
very fast and direct unless it rolled or until it hit a wall.

Planes/flying models with turned wingtips (esp down) or wingtip engines or pods to defeat
air from under the wing circling up over the tip do cut or eliminate that source of drag.

Even with no dihedral or anhedral wings you still get drag equal or more to holding the
plane up, the energy has to come from somewhere says Newton.

Picture on top and behind the wing two people playing tug of war. Over the wing is Low
Pressure (says on the shirt) and behind it is Down Wash. If either was not pulling, the
other would cease to exist.
If that doesn't make sense to you then go back and learn the parts of Newtons Laws that
you missed, action-reaction takes at least a pair of forces.

buzzsaw1939
02-15-2008, 05:32 AM
Gunz... I don't know why I have trouble understanding you some times (must be old brain cells) because I'm reading you load and clear now!

I'm actually learning some things I didn't know! thanks buddy! http://forums.ubi.com/images/smilies/25.gif

M_Gunz
02-15-2008, 09:25 AM
Back in 68, back in 6th grade, I got a book fair book by a guy named Ralph S. Barnaby (look
him up if you need to, the book has a pic of his pilot's license and the number is 2. He
was a kid who knew and did things for the Wrights. Orville or Wilbur got #1 and Ralph got
#2, guess what HE flew first? Anyway he shows really basic aero in his book How To Make
And Fly paper Airplanes including about vortex, dihedral and anhedral wings -- you can get
used copies for $1 or less through Amazon. That book got me started on more than just
building plastic models and watching planes every chance I got, IRL or on TV.
A few years later on a Brittanica dig about WWI fighters I learned that the SPAD wings are
supposed to be a 2 degree anhedral which did kill more trainees than flew the plane, you
can guess what a crosswind would do to such a light, low wing loaded plane! The Sopwith
Camel also killed more trainees than flew the plane but I'm not sure which was worse.
If I hadn't absorbed what Barnaby wrote, I might have missed the reference to the SPAD later,
I have yet to see a WWI sim SPAD with anhedral wings or any that had to be balanced so.
But it does explain a bit about the extreme for the time speeds that plane would go.

But I don't have 100 hours in the front seats of planes! I don't have the training to pull
the right circuit breakers in seconds in response to warning lights, though I do know some
of the training those who do repeatedly go through.

Holtzauge
02-15-2008, 09:28 AM
Originally posted by M_Gunz:
Wingtip vortexes are a result of wing dihedral, air flowing up along the wing underneath
instead of straight back.

I've made exactly two gliders that had slight anhedral wings and could when thrown carefully
indoors (no wind) fly straight. The glide path was extremely shallow compared to others,
very fast and direct unless it rolled or until it hit a wall.

Planes/flying models with turned wingtips (esp down) or wingtip engines or pods to defeat
air from under the wing circling up over the tip do cut or eliminate that source of drag.

Even with no dihedral or anhedral wings you still get drag equal or more to holding the
plane up, the energy has to come from somewhere says Newton.

Picture on top and behind the wing two people playing tug of war. Over the wing is Low
Pressure (says on the shirt) and behind it is Down Wash. If either was not pulling, the
other would cease to exist.
If that doesn't make sense to you then go back and learn the parts of Newtons Laws that
you missed, action-reaction takes at least a pair of forces.

Well, thanks for the lecture but you obviously have no idea what you are talking about.

Wingtip vortices are NOT a result of wing dihedral as you claim.

Wingtip vortices are caused by the the LIFT generated by the wing. A wing with NO dihedral will still shed wing tip vortices when generating lift.

M_Gunz
02-15-2008, 09:42 AM
EDIT: Okay, that first statement was in error and I should have written a bit different.

It will shed some. Higher pressure below flows around the tip and vortex.
The more dihedral you have, the more vortex you get. Wind does flow upwards.
With anhedral you get almost NONE, the flow blends in at the fuselage.
If you put a device like tip turned esp down at the tip then you stop most if not all vortex.

$#!+, I've BUILT and flown the models to check these things as I was taught, but I know nada?
What is your EXPERIENCE here?

EDIT: Oh BTW, you don't think that all lift drag is at the wingtips by any chance?

Holtzauge
02-15-2008, 10:13 AM
Originally posted by M_Gunz:
It will shed some. Higher pressure below flows around the tip and vortex.
The more dihedral you have, the more vortex you get. Wind does flow upwards.
With anhedral you get almost NONE, the flow blends in at the fuselage.
If you put a device like tip turned esp down at the tip then you stop most if not all vortex.

$#!+, I've BUILT and flown the models to check these things as I was taught, but I know nada?
What is your EXPERIENCE here?

EDIT: Oh BTW, you don't think that all lift drag is at the wingtips by any chance?

No, you are WRONG, you do not get almost NONE if you have anhedral. The MAIN effect is the wing LIFT which will still be there irrespective of anhedral/dihedral.

Concerning turning the wing up or down: Your claim that this "stop most if not all vortex" is ridiculous. Such a device is usually called a winglet and the effect is basically to increase the effective span corresponding to the length of the winglet.

Read some BASIC aerodynamics before you start lecturing next time.

BTW: Since you make insinuations about my EXPERIENCE as you put it I can tell you I have an Msc. in aeronautical engineering http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

"My view is that a little knowledge is a dangerous thing"

M_Gunz
02-15-2008, 02:23 PM
Originally posted by Holtzauge:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by M_Gunz:
It will shed some. Higher pressure below flows around the tip and vortex.
The more dihedral you have, the more vortex you get. Wind does flow upwards.
With anhedral you get almost NONE, the flow blends in at the fuselage.
If you put a device like tip turned esp down at the tip then you stop most if not all vortex.

$#!+, I've BUILT and flown the models to check these things as I was taught, but I know nada?
What is your EXPERIENCE here?

EDIT: Oh BTW, you don't think that all lift drag is at the wingtips by any chance?

No, you are WRONG, you do not get almost NONE if you have anhedral. The MAIN effect is the wing LIFT which will still be there irrespective of anhedral/dihedral. </div></BLOCKQUOTE>

What are you on about, VORTEX or DRAG?
I learned from Ralph Barnaby that using anhedral wings cut the vortex. The models with wing
tips lower than wing roots, anhedral, flew with much less drag than the ones with dihedral.


Concerning turning the wing up or down: Your claim that this "stop most if not all vortex" is ridiculous. Such a device is usually called a winglet and the effect is basically to increase the effective span corresponding to the length of the winglet.

No, the device I wrote about is NOT a winglet as it does NOT have camber for one.
On one site they call it an endplate.

As Barnaby showed and explained, higher pressure air from under the wing comes over the wing
tip and creates the spinning vortex behind the wingtip.
Solution: block the air from going around the end of the wing.
HOW? Put a surface at the end of the wing to stop the flow.


Read some BASIC aerodynamics before you start lecturing next time.

I have. They all give the SAME EXPLANATION he did for wingtip vortex generation.

In his book he stated that the air underneath the wing will flow upwards under the wing.

I haven't seen anything that says he is wrong except YOU.

Low and behold I see sites showing air on top of the wings flowing not straight back but
inwards while the air underneath flows not straight back but outwards. On wings with DIHEDRAL.

And a glider with shorter wings but with tips folded down does have a better glide angle and
flies farther than one with longer wings and straight tips. Almost like it has less drag.
The ones with anhedral flew even better and faster when I could balance them well enough to fly.

There's one site that explains the difference between infinitely long wing and finite length
wing is, get this --- higher pressure air coming up around the wingtip and creating a vortex.

Oh yes, there's also the man who designed the Flying Pancake back around 1930 who put the
engines and props on the wingtips to eliminate the vortex.

It really doesn't leave me much to disbelieve Ralph S. Barnaby on at all.


BTW: Since you make insinuations about my EXPERIENCE as you put it I can tell you I have an Msc. in aeronautical engineering http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif

Insinuation HELL. I asked.


"My view is that a little knowledge is a dangerous thing"

What, are my small gliders endangering anyone? Is someone going to design and build planes on
my say so? Will it affect global warming or prolong the war in Iraq? What danger?

Gee, my knowledge in the area of vortex did come from a very old source, perhaps you can explain
the results I got in terms of BASIC AERODYNAMICS that you feel I need to read? And you can
explain WHY an end plate on a wingtip won't reduce or eliminate the wingtip vortex?

Holtzauge
02-15-2008, 03:07 PM
M_Gunz: Laying smokescreens does not change the fact that your original claim about what causes the wing tip vortices: "Wingtip vortexes are a result of wing dihedral, air flowing up along the wing underneath instead of straight back." is untrue.

Likewize your claim that "With anhedral you get almost NONE, the flow blends in at the fuselage." is also totally wrong.

If you intend to lecture people from a high perch with statements like " If that doesn't make sense to you then go back and learn the parts of Newtons Laws that you missed, action-reaction takes at least a pair of forces." then get your facts right before you take the plunge.

Face it, you are WRONG here, no amount of wiggling or trying to change the subject will change that.

M_Gunz
02-15-2008, 09:19 PM
Fine. Set me right. Tell me where and why I have those things wrong.
You may note that I did more than tell someone to go study Newton, I provided some as well.
I didn't exactly point to any locked doors. Unless you're "insinuating" that I have.

So let's have it especially the part about what's really happening when I turn the wingtips
down on the model gliders so myself and the rest can know.

Does airflow under the wing tend to slide UPWARDS on wings with dihedral or anhedral?
You clearly seem to be saying no so please, what's going on there?
I dunno, maybe Viper, Ugly_Kid or Crumpp will come along and explain, they're good about that.

Holtzauge
02-16-2008, 03:30 AM
There are numerous ways to explain lift but the appealing thing about the lifting line theory and circulation is that they combine a mathematical model with what we can observe IRL in a nice way.

For starters, consider a wing with zero lift. There is no lift and no downwash. If we suddenly increase AoA on a wing we will actually observe a vortex shed behind the wing called the starting vortex. This will also be observable if we change AoA and a new vortex will be shed in the wake. The nice thing is that this can both be mathematically calculated and also observed.

Now a wing of finite span can be modelled mathematically by a number of bound vortexes that model the spanwise distribution of lift. Since the lift usually decreases from the root towards the tip there will be a continuous shedding of vortexes along the trailing edge. The effects of this can also be observed IRL since wool tufts on a wing topside will angle slighly inwards and on the lower side slightly outwards. Towards the tip the vortex sheet rolls together to form a strong vortex called the wingtip vortex.

Another nice aspect of the theory is that a flap deflection over a part of the span can be modelled as a strong additional vortex bound to that part of the wing. This gives us a discontinuity in the vortex sheet. Inboard of the flap the there is a stronger vortex than outside. This discontinuity can also be observed IRL when you fly in a passanger jet as a line of condensation flowing backwards from the outer flap joint (under the right atmospheric conditions). This is the center of the vortex shed as a result of the discontinuity in spanwise lift distribution.

The bound vortices will theoretically not only result in a downwash behind the wing but also in an upwash in front of the wing which again ties in nicely with what we can observe IRL and what the momemtum theory and Newton tells us.

All this will happen irrespective of anhedral/dihedral. The main factor here is the span and wing loading combined. Taking extremes, a glider has a low span loading leading to a vortex intensity that is distributed over a long span leading to a spred out sheet of low intensity vortices. A F-104 Starfighter OTOH can be modelled with a very concentrated vortex sheet with a large drop of lift toward the tip resulting in a humungous vortex at the tip. This vortex will be VERY strong irrespective of anhedral/dihedral. Of course the tip tanks on the F-104 have a positive effect on the induced drag but you will still get a very good approximation of the cost of lift by ONLY looking at an aircrafts span and wing loading.

Going back to endplates. Yes they can eliminate the vortex IF they are infinite large i.e. a wall. If they are anything smaller than that they will only distribute the shedding of vortices out along the endplates. IRL, they will thus cut down induced drag BUT they will increase skin friction drag etc and cost more drag than they cut which explains why there are no successful a/c with endplates. Note a/c NOT WIG's which are another matter entirely.

Winglets are a compromise between cutting vortexes and increased wetted area. Again, there is no such thing as a free lunch, and usually they will only give good results in a limited Cl range. This OTOH is OK for an airliner that operates at long times a certain lift conditions and the winglet can thus be optimised for this Cl range while accepting the detrimental effects in other flight conditions.

Bremspropeller
02-16-2008, 06:46 AM
Holtzauge, allow me to post some pics of what you just worote...

First, a 767 climbing away from the RWY.
You can clearly see the wingtip-vortices.
Note the high AoA! (angle between vortex and wing chord-line)
http://www.airliners.net/photo/Skymark-Airlines/Boeing-767-3Q8-ER/1325519/L/

Next, let me show you guys, what winglets are only optimized for a tight range of AoAs.
Naturally, that would be the AoAs of cruise.
This A330 shows that, upon rotating, the winglets will create lift, and therefore leave a trail of wingtip-vortices...
http://www.airliners.net/photo/BMI-British-Midland/Airbus-A330-243/1321377/L/

And at last, there's not only flaps and and wingtips, creating vortices.
The elvevator will also create a vortex at it's tip (depending on trim-setting; the further out of center, the more powerfull the vortex).
What you can also see here is the loss of pressure above the wing, creating the "mist" that can also be seen with a/c maneuvering hard (i.e. fighters) or flying close to Mach 1 in humid conditions.
http://www.airliners.net/photo/Qantas/Boeing-767-336-ER/1224429/L/
http://www.airliners.net/photo/KLM---Royal/McDonnell-Douglas-MD-11/1178748/L/

But there are other neat ways of producing (more) lift.
http://www.airliners.net/photo/First-Choice-Airways/Boe...67-324-ER/1164361/L/ (http://www.airliners.net/photo/First-Choice-Airways/Boeing-767-324-ER/1164361/L/)
Wonder where the vortex from beside the engine comes from?
http://www.airliners.net/photo/American-Airlines/Boeing-767-323-ER/0984220/L/

Well, there is a little vortex-generator, called "strake", that creates a high-energy vortex that increases lift over the wing.
The LERX of modern fighters work the same way..
This F-18 shows how those strakes/ LERX work:
http://www.airliners.net/photo/USA---Navy/McDonnell-Douglas-F-A-18C/1047708/L/

buzzsaw1939
02-16-2008, 07:20 AM
Holzauge... You know damn well you and gunz are talking about the same thing, lighten up will ya?

You were able to go to school, he's self tought, and damn well I might add!

Strikes me you've been lurking and just waiting for him to make a mistake, and have jumped to some conclusions about his explantions, I don't see him claiming to be an expert, he's trying to help, in lymans terms.

If your interested in helping here, I would like to here some more of your imput, not attacks, gains nothing!

M_Gunz
02-16-2008, 07:43 AM
Originally posted by Holtzauge:
There are numerous ways to explain lift but the appealing thing about the lifting line theory and circulation is that they combine a mathematical model with what we can observe IRL in a nice way.

For starters, consider a wing with zero lift. There is no lift and no downwash. If we suddenly increase AoA on a wing we will actually observe a vortex shed behind the wing called the starting vortex. This will also be observable if we change AoA and a new vortex will be shed in the wake. The nice thing is that this can both be mathematically calculated and also observed.

Now a wing of finite span can be modelled mathematically by a number of bound vortexes that model the spanwise distribution of lift. Since the lift usually decreases from the root towards the tip there will be a continuous shedding of vortexes along the trailing edge. The effects of this can also be observed IRL since wool tufts on a wing topside will angle slighly inwards and on the lower side slightly outwards. Towards the tip the vortex sheet rolls together to form a strong vortex called the wingtip vortex.

Another nice aspect of the theory is that a flap deflection over a part of the span can be modelled as a strong additional vortex bound to that part of the wing. This gives us a discontinuity in the vortex sheet. Inboard of the flap the there is a stronger vortex than outside. This discontinuity can also be observed IRL when you fly in a passanger jet as a line of condensation flowing backwards from the outer flap joint (under the right atmospheric conditions). This is the center of the vortex shed as a result of the discontinuity in spanwise lift distribution.

The bound vortices will theoretically not only result in a downwash behind the wing but also in an upwash in front of the wing which again ties in nicely with what we can observe IRL and what the momemtum theory and Newton tells us.

All this will happen irrespective of anhedral/dihedral. The main factor here is the span and wing loading combined. Taking extremes, a glider has a low span loading leading to a vortex intensity that is distributed over a long span leading to a spred out sheet of low intensity vortices. A F-104 Starfighter OTOH can be modelled with a very concentrated vortex sheet with a large drop of lift toward the tip resulting in a humungous vortex at the tip. This vortex will be VERY strong irrespective of anhedral/dihedral. Of course the tip tanks on the F-104 have a positive effect on the induced drag but you will still get a very good approximation of the cost of lift by ONLY looking at an aircrafts span and wing loading.

Going back to endplates. Yes they can eliminate the vortex IF they are infinite large i.e. a wall. If they are anything smaller than that they will only distribute the shedding of vortices out along the endplates. IRL, they will thus cut down induced drag BUT they will increase skin friction drag etc and cost more drag than they cut which explains why there are no successful a/c with endplates. Note a/c NOT WIG's which are another matter entirely.

Winglets are a compromise between cutting vortexes and increased wetted area. Again, there is no such thing as a free lunch, and usually they will only give good results in a limited Cl range. This OTOH is OK for an airliner that operates at long times a certain lift conditions and the winglet can thus be optimised for this Cl range while accepting the detrimental effects in other flight conditions.

Thank You Very Much!

It leaves me scratching my head at the results of the model gliders but maybe some day I'll
get what's going on there. On a full sized glider my endplates would be maybe 2+ ft down
and perhaps a very slow, very light glider gets different results or the answer is completely
different.

I was sure before that there is turbulence all behind the wing, and downwash = lift or else
how can the plane stay up?

The no free lunch is a given and not just in physical energy. When I developed code I had
to tell some clients that a given task takes at least a certain amount of work but if they
really wanted to direct what they didn't understand it could take a hell of a lot more.
In AC terms you could say that some ways to fly are less efficient but there is no magic.

Well I can forget that part of what I learned from Captain Barnaby, but I still respect him!

Holtzauge
02-16-2008, 07:53 AM
Originally posted by Bremspropeller:
Holtzauge, allow me to post some pics of what you just worote...

First, a 767 climbing away from the RWY.
You can clearly see the wingtip-vortices.
Note the high AoA! (angle between vortex and wing chord-line)
http://www.airliners.net/photo/Skymark-Airlines/Boeing-767-3Q8-ER/1325519/L/

Next, let me show you guys, what winglets are only optimized for a tight range of AoAs.
Naturally, that would be the AoAs of cruise.
This A330 shows that, upon rotating, the winglets will create lift, and therefore leave a trail of wingtip-vortices...
http://www.airliners.net/photo/BMI-British-Midland/Airbus-A330-243/1321377/L/

And at last, there's not only flaps and and wingtips, creating vortices.
The elvevator will also create a vortex at it's tip (depending on trim-setting; the further out of center, the more powerfull the vortex).
What you can also see here is the loss of pressure above the wing, creating the "mist" that can also be seen with a/c maneuvering hard (i.e. fighters) or flying close to Mach 1 in humid conditions.
http://www.airliners.net/photo/Qantas/Boeing-767-336-ER/1224429/L/
http://www.airliners.net/photo/KLM---Royal/McDonnell-Douglas-MD-11/1178748/L/

But there are other neat ways of producing (more) lift.
http://www.airliners.net/photo/First-Choice-Airways/Boe...67-324-ER/1164361/L/ (http://www.airliners.net/photo/First-Choice-Airways/Boeing-767-324-ER/1164361/L/)
Wonder where the vortex from beside the engine comes from?
http://www.airliners.net/photo/American-Airlines/Boeing-767-323-ER/0984220/L/

Well, there is a little vortex-generator, called "strake", that creates a high-energy vortex that increases lift over the wing.
The LERX of modern fighters work the same way..
This F-18 shows how those strakes/ LERX work:
http://www.airliners.net/photo/USA---Navy/McDonnell-Douglas-F-A-18C/1047708/L/

Beautiful photos Bremspropeller. I think they illustrate the point very well.

You can see the vortex at the flap junction well and you can also see how the center of the wing tip vortex is moved upwards/outwards by the winglet which increases the effective span.

About the vortex coming of the elevator/stabilator: The price you pay for flap deflection and increased lift is a severe nose-down pitching momement which needs to be balanced by an increasing elevator/stabilator download as the flap angle goes up which shows up nicely at the elevator tips.

About the vortex coming off from the front close to the engine: My guess is that this originates between the nose slats which probably are split by the engine gondola which leads to a discontinuity in the lift which then results in a vortex.

Last but not least: there are two fundamentally different ways ways to generate lift: One is the circulation lift we have been discussion here. Another is vortex lift which is effective up to high angles of attack but is very costly in terms of lift generated drag. At low to moderate AoA the F-18 will generate a lot of lift based on circulation but as AoA goes up this diminishes and the vortex generated lift does most of the work which is nicely illustrated by the picture.

I would venture a guess that at design cruise conditions the F-18's strake will be formed so as to be unloaded so that no drag inducing vortex is generated.

Holtzauge
02-16-2008, 08:09 AM
Originally posted by M_Gunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Holtzauge:
There are numerous ways to explain lift but the appealing thing about the lifting line theory and circulation is that they combine a mathematical model with what we can observe IRL in a nice way.

For starters, consider a wing with zero lift. There is no lift and no downwash. If we suddenly increase AoA on a wing we will actually observe a vortex shed behind the wing called the starting vortex. This will also be observable if we change AoA and a new vortex will be shed in the wake. The nice thing is that this can both be mathematically calculated and also observed.

Now a wing of finite span can be modelled mathematically by a number of bound vortexes that model the spanwise distribution of lift. Since the lift usually decreases from the root towards the tip there will be a continuous shedding of vortexes along the trailing edge. The effects of this can also be observed IRL since wool tufts on a wing topside will angle slighly inwards and on the lower side slightly outwards. Towards the tip the vortex sheet rolls together to form a strong vortex called the wingtip vortex.

Another nice aspect of the theory is that a flap deflection over a part of the span can be modelled as a strong additional vortex bound to that part of the wing. This gives us a discontinuity in the vortex sheet. Inboard of the flap the there is a stronger vortex than outside. This discontinuity can also be observed IRL when you fly in a passanger jet as a line of condensation flowing backwards from the outer flap joint (under the right atmospheric conditions). This is the center of the vortex shed as a result of the discontinuity in spanwise lift distribution.

The bound vortices will theoretically not only result in a downwash behind the wing but also in an upwash in front of the wing which again ties in nicely with what we can observe IRL and what the momemtum theory and Newton tells us.

All this will happen irrespective of anhedral/dihedral. The main factor here is the span and wing loading combined. Taking extremes, a glider has a low span loading leading to a vortex intensity that is distributed over a long span leading to a spred out sheet of low intensity vortices. A F-104 Starfighter OTOH can be modelled with a very concentrated vortex sheet with a large drop of lift toward the tip resulting in a humungous vortex at the tip. This vortex will be VERY strong irrespective of anhedral/dihedral. Of course the tip tanks on the F-104 have a positive effect on the induced drag but you will still get a very good approximation of the cost of lift by ONLY looking at an aircrafts span and wing loading.

Going back to endplates. Yes they can eliminate the vortex IF they are infinite large i.e. a wall. If they are anything smaller than that they will only distribute the shedding of vortices out along the endplates. IRL, they will thus cut down induced drag BUT they will increase skin friction drag etc and cost more drag than they cut which explains why there are no successful a/c with endplates. Note a/c NOT WIG's which are another matter entirely.

Winglets are a compromise between cutting vortexes and increased wetted area. Again, there is no such thing as a free lunch, and usually they will only give good results in a limited Cl range. This OTOH is OK for an airliner that operates at long times a certain lift conditions and the winglet can thus be optimised for this Cl range while accepting the detrimental effects in other flight conditions.

Thank You Very Much!

It leaves me scratching my head at the results of the model gliders but maybe some day I'll
get what's going on there. On a full sized glider my endplates would be maybe 2+ ft down
and perhaps a very slow, very light glider gets different results or the answer is completely
different.

I was sure before that there is turbulence all behind the wing, and downwash = lift or else
how can the plane stay up?

The no free lunch is a given and not just in physical energy. When I developed code I had
to tell some clients that a given task takes at least a certain amount of work but if they
really wanted to direct what they didn't understand it could take a hell of a lot more.
In AC terms you could say that some ways to fly are less efficient but there is no magic.

Well I can forget that part of what I learned from Captain Barnaby, but I still respect him! </div></BLOCKQUOTE>

Your'e welcome!

The anhedral may do something for the model gliders that is not directly applicable to full size airplanes. There may be effects here that have to do with Reynolds number which would be quite different for a model glider and an aircraft.

I think the golf ball dimples are a good example of this. Things are not always what they intuitively appear in areodynamics...

Bremspropeller
02-16-2008, 08:11 AM
Strake on a 737 classic:

http://www.airliners.net/photo/Norwegian-Air-Shuttle/Boeing-737-3L9/1275157/L/


Thrust rev, flaps and ground-spoilers deployed.

M_Gunz
02-16-2008, 08:30 AM
Originally posted by buzzsaw1939:
Holzauge... You know damn well you and gunz are talking about the same thing, lighten up will ya?

You were able to go to school, he's self tought, and damn well I might add!

Strikes me you've been lurking and just waiting for him to make a mistake, and have jumped to some conclusions about his explantions, I don't see him claiming to be an expert, he's trying to help, in lymans terms.

If your interested in helping here, I would like to here some more of your imput, not attacks, gains nothing!

Nah nah Buzz! Honest, he's fixed me on some detail I had wrong --- I'm 99% sure!

And I did get some teaching given here and there too, just nowhere near as much in many subjects
as I wanted so yes I went out and learned since after all the teachers in our school said the
main goal was for us to be able to learn on our own. It's stood by me all my life since but
I have still gone and taken courses here and there... to 'legitimize' my resumes on work I had
done and been paid for before I took the courses and it did help get contracts. An education
is a good starting point in many careers where otherwise you'd be lost or playing catch-up.

Yer right though, I don't claim aero expertise! I do claim to know a thing or two but every
so often I find out different -- that's life, live and learn when possible! Find me someone
who knows everything and I'll show you someone who's done little if anything. ;^) True!

The thing is that I welcome chance to learn for real (and always did or I'd be a dummy) and
he's been good enough to do that without talking over my head, so I'm very thankful and hope
such continues.

M_Gunz
02-16-2008, 08:41 AM
S! Brems, for a while there I thought maybe they were somehow blowing bypass air over the wing!
I mean, you did write there's ways to get extra lift and that would be a Coanda kind of thing.
But that wouldn't make sense for at least 2 reasons, would it? Heat and drag?

Do you have any pics like those of any high wing planes with anhedral? There's supposed to
be quite a few out there or at least discussions I've looked at name some.

Bremspropeller
02-16-2008, 08:49 AM
BAe 146 http://www.flugzeug-bild.de/bilder/bae-146-668.jpg

MDD C-17
http://www.globalaircraft.org/photos/planephotos/c-17-1.jpg

Lockheed C-5 Galaxy
http://www.aviationexplorer.com/aircraft_thumbs/c5_3.jpg

Lockheed C-141 Starlifter
http://www.aviationexplorer.com/aircraft_thumbs/c141_1.jpg

Antonov An-124
http://www.suchoj.com/andere/An-124/images/An-124_10.jpg

...to name a few.


That bypass-air thingy was made on several a/c - the air was caught from some compressor-stage in the engine.
The F-4 (non maneuver-slat a/c) for example had BLC (boundary layer control" on the leading-edge droops, as well as on the trailing-edge flaps!

M_Gunz
02-16-2008, 09:20 AM
On the jets I sat in class and wrote systems training apps for they got pneumatic pressure
from bleed-air which IIRC was supposed to be something to do with bypass, but that's all the
detail the courses and manuals gave. And sure enough someone has used it externally.

I was hoping for the takeoff type pics with the contrails just to show how wrong I was! LOL!
It's no worse than being shot down online, IMO. http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif Been there, done it, made no excuses.

Holtzauge
02-16-2008, 09:57 AM
Originally posted by M_Gunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by buzzsaw1939:
Holzauge... You know damn well you and gunz are talking about the same thing, lighten up will ya?

You were able to go to school, he's self tought, and damn well I might add!

Strikes me you've been lurking and just waiting for him to make a mistake, and have jumped to some conclusions about his explantions, I don't see him claiming to be an expert, he's trying to help, in lymans terms.

If your interested in helping here, I would like to here some more of your imput, not attacks, gains nothing!

Nah nah Buzz! Honest, he's fixed me on some detail I had wrong --- I'm 99% sure!

And I did get some teaching given here and there too, just nowhere near as much in many subjects
as I wanted so yes I went out and learned since after all the teachers in our school said the
main goal was for us to be able to learn on our own. It's stood by me all my life since but
I have still gone and taken courses here and there... to 'legitimize' my resumes on work I had
done and been paid for before I took the courses and it did help get contracts. An education
is a good starting point in many careers where otherwise you'd be lost or playing catch-up.

Yer right though, I don't claim aero expertise! I do claim to know a thing or two but every
so often I find out different -- that's life, live and learn when possible! Find me someone
who knows everything and I'll show you someone who's done little if anything. ;^) True!

The thing is that I welcome chance to learn for real (and always did or I'd be a dummy) and
he's been good enough to do that without talking over my head, so I'm very thankful and hope
such continues. </div></BLOCKQUOTE>

M_Gunz: I have read your posts in other threads and I'm aware that you have a good grasp of science. I respect when someone can admit they need to reevaluate their stance on an issue and move on.
S!

Holtzauge
02-16-2008, 10:08 AM
Originally posted by Bremspropeller:
Strake on a 737 classic:

http://www.airliners.net/photo/Norwegian-Air-Shuttle/Boeing-737-3L9/1275157/L/


Thrust rev, flaps and ground-spoilers deployed.

That's intersting with the strake. If that is also present on the a/c you posted before with the vortex contrail over the wing at the engine this gives a good explanation for it showing up where it did.

I wonder why they put that strake there on the 737 and perhaps on the other a/c as well....

M_Gunz
02-16-2008, 11:59 AM
Originally posted by Holtzauge:
I think the Kutta condition (see link) and the circulation concept is useful. The circulation concept explains the vortice shedding along the wing and the massive lift induced vortices at each wing tip. Also: a wing in inviscous flow would not provide lift because the air would sneak back up the trailing edge and no lift would be produced. So don't curse viscosity (i.e drag) but be thankful every time you take off! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Kutta condition: http://en.wikipedia.org/wiki/Kutta_condition

So I read through looking for "where is the lift" and see stagnation points and how the sharp
trailing edge moves the rear stagnation point down but still not the lift and then I read about
the circulation and get into Kutta-Joukowski and what do I find?

Kutta-Joukowski Theorem (http://en.wikipedia.org/wiki/Kutta-Joukowski_Theorem)

Formal proof of the theorem is to be found in standard texts (see eg ref. 1, p 406). However as a plausibility argument, consider a thin airfoil of chord c and infinite span, moving through air of density ρ. Let the airfoil be inclined to the oncoming flow to produce an average air speed V on one side of the airfoil, and an average air speed V + ΔV on the other side. The circulation is then

Γ = (V + ΔV)c − (V)c = ΔVc

The difference in pressure ΔP between the two sides of the airfoil can be found by applying Bernoulli's equation:

It's almost like the Kutta-Joukowski Theorem is a full explanation of how we get the pressure
difference ala Bernoulli into place.... ?

Holtzauge
02-16-2008, 02:16 PM
Originally posted by M_Gunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Holtzauge:
I think the Kutta condition (see link) and the circulation concept is useful. The circulation concept explains the vortice shedding along the wing and the massive lift induced vortices at each wing tip. Also: a wing in inviscous flow would not provide lift because the air would sneak back up the trailing edge and no lift would be produced. So don't curse viscosity (i.e drag) but be thankful every time you take off! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Kutta condition: http://en.wikipedia.org/wiki/Kutta_condition

So I read through looking for "where is the lift" and see stagnation points and how the sharp
trailing edge moves the rear stagnation point down but still not the lift and then I read about
the circulation and get into Kutta-Joukowski and what do I find?

Kutta-Joukowski Theorem (http://en.wikipedia.org/wiki/Kutta-Joukowski_Theorem)

Formal proof of the theorem is to be found in standard texts (see eg ref. 1, p 406). However as a plausibility argument, consider a thin airfoil of chord c and infinite span, moving through air of density ρ. Let the airfoil be inclined to the oncoming flow to produce an average air speed V on one side of the airfoil, and an average air speed V + ΔV on the other side. The circulation is then

Γ = (V + ΔV)c − (V)c = ΔVc

The difference in pressure ΔP between the two sides of the airfoil can be found by applying Bernoulli's equation:

It's almost like the Kutta-Joukowski Theorem is a full explanation of how we get the pressure
difference ala Bernoulli into place.... ? </div></BLOCKQUOTE>

Yep, looks like we turned full circle. Bernoulli and Kutta-Joukowski....

You can't have one without the other http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

Patriot_Act
02-16-2008, 05:13 PM
Originally posted by Patriot_Act:
The C-17 has a supercritical airfoil.
(nice photo by the way)
The bottom surface has as long a path from
leading edge centerline to the trailing edge
as the upper surface.
And dang it,,,, that photo proves it can fly.

In a supercritical airfoil there is a concave
form just before the trailing edge to change
the airflow to make the top and bottom surface
flow meet at the same time.
This nearly eliminates the nasty shock wave that
forms on the top surface about 3/4 chord width back from the leading edge.

This makes a supercritical airfoil very efficent at all speeds
even trans sonic speeds.

P.A.

M_Gunz
02-16-2008, 11:49 PM
Originally posted by Holtzauge:
Yep, looks like we turned full circle. Bernoulli and Kutta-Joukowski....

You can't have one without the other http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

You can, it just doesn't explain how lift works, IMO.

The only ways I know to move or lift objects beyond the atomic scale involve fields or touching.
Pressure differences are touching and it was Bernoulli who gave us those equations.

At the atomic level it's all fields working on electron shells last I heard, no matter that the
shells are tied to the nucleus it would take Raaaid or Josf to go to that level.

The last I looked, Coanda did not rewrite pressure equations. Air following the surface and
AOA lead us to Bernoulli's pressure equations no matter who explained about air following the
surface. NEITHER of those guys Invented anything that didn't happen already AFAIK.

M_Gunz
02-16-2008, 11:52 PM
Originally posted by Patriot_Act:
Originally posted by Patriot_Act:
The C-17 has a supercritical airfoil.
(nice photo by the way)
The bottom surface has as long a path from
leading edge centerline to the trailing edge
as the upper surface.
And dang it,,,, that photo proves it can fly.


Down to quoting yourself, I see.

Give thin flat plates some AOA and power and they do fly too. Proved. Big deal.

Holtzauge
02-17-2008, 03:50 AM
Originally posted by M_Gunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Holtzauge:
Yep, looks like we turned full circle. Bernoulli and Kutta-Joukowski....

You can't have one without the other http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

You can, it just doesn't explain how lift works, IMO.

The only ways I know to move or lift objects beyond the atomic scale involve fields or touching.
Pressure differences are touching and it was Bernoulli who gave us those equations.

At the atomic level it's all fields working on electron shells last I heard, no matter that the
shells are tied to the nucleus it would take Raaaid or Josf to go to that level.

The last I looked, Coanda did not rewrite pressure equations. Air following the surface and
AOA lead us to Bernoulli's pressure equations no matter who explained about air following the
surface. NEITHER of those guys Invented anything that didn't happen already AFAIK. </div></BLOCKQUOTE>

Sorry if I lost you there. I was just trying to apply a little EQ and made a reference to Frank Sinata:

"Love and marriage,
love and marriage
Go together like a horse and carriage
This I tell you brother
You can't have one without the other"

I did not imply the connection scientifically. I think the Bernouilli way of explaining lift is OK for flight schools.

I have worked as a glider instructor and I can tell you that the concepts of circulation, Prandtl lifting line theory and bound vortices are not suitable way's to explain lift to some of the flight students I've met in my time....

Holtzauge
02-17-2008, 04:02 AM
Originally posted by M_Gunz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Patriot_Act:
Originally posted by Patriot_Act:
The C-17 has a supercritical airfoil.
(nice photo by the way)
The bottom surface has as long a path from
leading edge centerline to the trailing edge
as the upper surface.
And dang it,,,, that photo proves it can fly.


Down to quoting yourself, I see.

Give thin flat plates some AOA and power and they do fly too. Proved. Big deal. </div></BLOCKQUOTE>

When I was studying aerodynamics in the 80' there was a joke going around and it goes like this:

Do you understand how American (US) aerodynamics work?

When the answer is no, you reply:

"Add more power!"

I think it's a very good joke. It captures the European view of how some people in the US approach things not only pratically but also sadly, lately, world affairs.....

M_Gunz
02-17-2008, 06:04 AM
Originally posted by Holtzauge:
You can't have one without the other"

Know the song from way back, really liked it being used for "Married With Children".


I did not imply the connection scientifically.

Well here I think it should because Bernoulli Principle does not bring AOA to the party.
Kutta-Joukowski brings that and more, the downwash and upwash and turbulence and circulation!


I think the Bernouilli way of explaining lift is OK for flight schools.

I have worked as a glider instructor and I can tell you that the concepts of circulation, Prandtl lifting line theory and bound vortices are not suitable way's to explain lift to some of the flight students I've met in my time....

I struggle with circulation. I haven't done that level math in almost 20 years and back then
I was over 30 and it wasn't fun any more. I know it is some fiction, the air from behind
the wing does not circle underneath and around to the front! But is is a very useful fiction
as really all science is, IMO.

In 75 the head of the Chemistry Dept at Drexel gave us our first lecture beginning saying
"Who here believes in electrons, protons and neutrons?". About half the class did but even
then I did not. So many hands in the air, he said "I do not believe in electrons, protons
and neutrons.". So okay, he understood Shroedinger and I am sure far better than I did or
ever will. He spoke of science as a model which I had also heard before. The model changes
from time to time but in the eyes of perhaps a majority it is always completely right.

Burke did a series in the mid 80's titled "The Day The Universe Changed" and in the 10th,
last, episode he gets the point across so well and solid that well, how can there be doubt?
Yeah, I know, the really stubborn ones could doubt gravity while falling. Or burn witches
over animals falling sick since it's real to them that the witches are the cause. We get
more of that here all the time, if they can just make everyone ACT like it's the 50's then
we'd have all else like it was then too. Just a lot of Peter Pan's and Wendies, IMO.

julian265
02-17-2008, 06:07 AM
Indoctrination - when people will argue as if the things they've been taught are the only correct explanations, despite not having either first hand experience, or a thorough feel for the topic. No, you don't get a thorough feel for lift production by flying, nor can you have first hand experience with inter-molecular forces.

Welcome to discussions of religion and the 'real life' handling of various second war aircraft. All arguments about things which are not known, in the true meaning of the word.